Method of centrifugal casting



Patented May 20, 1941 UNITED. STATES PATENT OFFICE METHOD or CENTRIFUGALCASTING Walter G. Donald, Cambridge, and James'L.

Martin, Lowell, Mass.

No Drawing. Application December 19 Serial No. 246,646

5 Claims.

The invention described herein may be manufactured and used by or forthe Government for (Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 0.6. 757) governmental purposes, without thepayment to side diameter or equivalent wall thickness which class willhereinafter be referred to generally as thick-walled cylinders orcastings.

Heretofore, where the need has arisen for thick walled cylinders orcastings capable of at once withstanding high pressures and offering ,awear and corrosion resistant interior surface, 'it has been necessary toeither compromise on a single material not complying with the fullrequirements of the need, or to use concentrically bonded materialswherein trouble has been'experienced in obtaining a satisfactory bond.

This necessity has existed because of the dimculty in avoidingsegregation during freezing of the large volume of metal used inthick-walled cylinders, or similar castings which causes the actualcomposition of the metal to widely vary in different. portions of thecasting. If the molten metal or heat is poured into an ordinarystationary chill mold of a size to give a thickwalled casting of anyappreciable length, both longitudinal and transverse segregation resultswhich is either exceedingly difficult or impossible to control withineconomically feasible limits,

this being especially true of longitudinal segregation. On the otherhand longitudinal segregation is avoided in the usual centrifugal castiron castings as made in the art at present, but such castings are sorelatively thin-walled that little if any gradient of composition of anytype results in the casting, consequently the fabrication of athick-walled cylindrical or similar member of two or more such castingsconcentrically or contiguously arranged does not result in a structurehaving a uniformgradient from the outer surface of the casting to thebore or inner side thereof.

It is an object of this invention to set forth a method for castingthick-walled cast iron cylindrical or similar castings whichincorporates steps heretofore employed for chilling the surfaces ofsimilar castings of short length; such as railway car wheels and millrolls, with present known centrifugal casting methods, in order toeliminate longitudinal segregation, and thereby render available an.economical method of producing castings of this class in substantiallengths.

It is a further object of this invention to co trol the radialsegregation of carbon in thickwalled centrifugal castings by controllingthe amount of carbon in the composition of metal being cast. to effect apredetermined gradient from white iron to gray iron.

While the essential objects and steps of this invention have beenoutlined above the same consists particularly in the steps to behereinafter set forth, it being understood however, that the descriptionis for the purpose of illustration and not limitation.

If a thick-walled cast iron cylinder or similar casting be castcentrifugally in a horizontally disposed cylindrical or otherappropriate chill mold spun about its longitudinal axis under conditionsinsuring a continuous uniform flow of molten metal throughout the fulllength of the mold, longitudinal segregation will be eliminated due tothe radial action of centrifugal force upon the flowing metal. At thesame time, however, due to the solidification process and/or centrifugalforce radial segregation of the carbon and other elements or impuritieswill be effected, and it is the control of this radial segregation ofcarbon, through a control of the total carbon content of the compositionbeing cast that we have provided for regulating the gradient from whiteiron to gray iron in thick-walled cylindrical or similar castings.

We have found that since segregation is not due to centrifugal forcealone; but, is also effected by the solidification process through whichthe molten metal passes in freezing, that there are several factors inany given set of conditions affecting the solidification-process thatmust be maintained constant in order to obtain a desired gradient fromwhite iron to gray iron solely through control of the total carbon inthe" cornpractically all gray iron with approximately 4.0% I

carbon may be cast in accordance with a predetermined specificationthrough control of the carbon contentof the molten metal to be cast. BYincreasing the carbon in steps above 2.5%, the outer white iron ring orzone becomes less in depth and the inner gray iron ring or zone becomescorrespondingly greater in depth, owing to the fact that the carbon isphysically displaced inwardly by the process of solidification andcentrifugal force.

The method of this invention avoids or eliminates the longitudinal ortop segregation characteristic of castings made in stationary chillmolds, provides castings having the desirable density characteristic ofcentrifugal castingaand teaches a method of coordinating the radialsegregating action of centrifugal force and the solidification processfor a more accurate control of the radial carbon gradient than hashitherto" been possible.

As examples of the control that may be attained of the depth of thewhite iron ring or zone, through variation in the total carbon contentof the melt alone, when the remaining factors above enumerated are keptconstant the following is given for a composition which except forcarbon is otherwise constant.

It will be noted that the depth of the white iron ring or zone ischanged through a control of total carbon alone and that it is notnecessary to otherwise relatively change the proportions of the siliconand sulphur with respect to the carbon to regulate this ring or zone.

Having thus described our invention, what we claim and desire to secureby Letters Patent is:

We claim:

1. In the method of centrifugally chill casting thick-walled cast ironcastings of the class having an outside diameter of four to six timesthe inside diameter and of appreciable length and uniform compositionexcept as to carbon and predetermining the depth of white iron zoneformed 2. In the method of centrifugally chill casting thick-walled castiron castings of the class having an outside diameter of 4 to 6 timesthe inside diameter and of uniform composition except as to carbon andpredetermining the depth of white 1 ,iron zone formed therein throughregulation of the carbon content of the iron to be cast alone, the stepswhich comprise selecting a rotating chill mold having itscross-sectional area proportioned with respect to the cross-sectionalarea of the casting in a chill ratio adapted to dissipate heat therefromat a rate effective to control radial segregation of carbon in a castingof the class recited varying from all white iron with 2.5% carbon tosubstantiallyall gray iron with 4.0% carbon, correlating the carboncontent of an iron with the depth of whiteiron zone predetermined forthe casting and the chill ratio between the limits of 2.5% and 4.0%,introducing said iron in the mold, and maintaining rotation of the molduntil solidification-of the casting.

3. In the method of forming cast iron cylindrical tubular articles ofthe class having an outside diameter of 4 to 6 times the insidediameter, the steps which comprise providing a rotatable chill moldhaving its cross-sectional area proportioned with respect to the'crosssectional area of a tubular article of said diameters in a ratio betweenthe limits of 65:1 and 1:1, selecting a cast iron, solely regulating thecarbon-content of said iron to a point between the limits of 2.5% to4.0% in accordance with said ratio and a predetermined depth of Whiteiron zone to be formed in the article between the limits of 0% and 100%,rotating the mold, and pouring said iron in molten form into the mold ata constant temperature.

4. In the method of forming cast iron cylindrical tubular articles ofthe class having an outside diameter of 4 to 6 times the insidediameter, the steps which comprise providing a rotatable chill moldhaving its cross-sectional area proportioned with respect to thecross-sectional area of a tubular article of said diameters in a ratioof 6.5:1, selecting a cast iron, solely regulating the carbon content ofsaid iron to a point between the limits of 2.5% to 4.0% in accordancewith said ratio and a predetermined depth of white iron zone to beformed in the article between the limits of 0% and 100%, rotating themold, and

thereinthrough regulation of the carbon content of the iron to be cast,the steps which comprise employinga horizontally disposed chillmoldrotating on its longitudinal axis and having a crosssectional area withrespect to the cross-sectional area of the casting proportioned in theratio of 6.5:1 to dissipate heat therefrom at a rate effective tocontrol radial segregationof carbon in a casting of the class recitedvarying from all white iron with 2.5% carbon to substantially all gray aconstant temperature.

- content of theiron to a point between the limits of 2.70% to 3.65% incorrelation with a predetermined depth of white iron zone to be formedin the article between the limits of 2.0 inches and 1.55 inches and sellratio of 6.5:1, rotating the mold, and pouring said iron in molten forminto the mold at a temperature of 2950 F.

WALTER G. DONALD.

JAMES L. MARTIN.

